Dispelling Myths about Male and Female Infertility
What does infertility really mean?
Technically, infertility does not mean the inability to conceive at all, but the inability to conceive within an expected time frame. The most common definition of infertility is the inability to conceive after 1 year of unprotected sex. Men and women can also take longer than expected to conceive, but if they still conceive within a year, they are considered "subfertile," rather than infertile.
- How old can you be and still conceive?
- Are men more or less likely than women to contribute to a couple's infertility?
- Does getting a regular period mean you're fertile?
Providing answers to the many common questions about infertility is one aim of National Infertility Awareness Week, observed April 20–26 this year. Common misunderstandings include the very nature of infertility itself: What is it? How common is it? What really causes it?
In keeping with this year's theme—"resolve to know more"—Drs. Stuart B. Moss and Susan Taymans, program officers in the NICHD's Fertility and Infertility Branch, answered questions about both male and female infertility—their respective areas of expertise—and discussed where infertility research is leading.
"Right now in the United States, about 7% to 10% of couples are infertile, which might not sound like much until you realize that diabetes, which is a disease that we think of as being very prevalent, affects about 8% of the United States population," Dr. Taymans said.
Myths about male and female infertility persist. For example, many people mistakenly believe that when a couple is infertile, it is probably due to the woman. In fact, when a couple is infertile, the cause is nearly as likely to be traced to the man as to the woman.
Age: A Major Contributing Factor
Age is a common factor in infertility, but it might not be clear exactly when fertility ebbs—or why.
Women are born with a finite supply of eggs. With age, that supply becomes depleted, and fertility declines until the woman is no longer able to support a pregnancy.
"Even though most women don't start menopause until about the age of 50, their fertility is really trailing off 10 years before their menopause," Dr. Taymans said. One NICHD-funded study found that, as women age, their egg cells suffer DNA damage and may die off because the cells' DNA repair systems wear out. Defects in one of the DNA repair genes, BRCA1, have been linked with breast cancer and now also seem to be involved in early menopause. (Read A Molecular Explanation for Age-related Fertility Decline in Women)
Men continue to produce sperm as they age, but sperm quality typically declines.
Stories of celebrities who become pregnant in their 40s may leave the impression that women can easily become pregnant at that age and older. And stories of children conceived through assisted reproductive technology (ART) may suggest that the process is an easy option.
"It's important to know that in cases of women getting pregnant in their 40s, there are a lot of underlying variables that you're just not seeing," Dr. Taymans said. It is important that women and men who are considering this option understand it more fully, including its cost and its likelihood of success.
Factors of Lifestyle and Environment
In addition to age, researchers have linked many other factors to infertility, including lifestyle factors that men and women may be able to control. Maintaining a healthy weight—being neither overweight nor underweight—and not smoking are two known factors that influence fertility. Genes may also play an important role. (Read Preconception stress increases the risk of infertility: results from a couple-based prospective cohort study--the LIFE study)
Exposure to some substances has also been associated with longer time to pregnancy. One study funded by the NICHD recently found that women whose male partners have high concentrations of three common forms of phthalates, chemicals found in a wide range of consumer products, take longer to become pregnant than do women in couples in which the male does not have high concentrations of those chemicals. (Read High Plasticizer Levels in Males Linked to Delayed Pregnancy for Female Partners)
There is still much to learn about male and female infertility, Drs. Moss and Taymans noted. For example, one-half of all cases of infertility among men have no known cause.
A Marker for Health
Infertility can be a sign of more general health problems, too.
"In large epidemiological studies, infertility has been linked to various cancers, to cardiovascular disease, and to diabetes and obesity," Dr. Moss said. "Clearly, there is, on some level, a correlative link."
One indicator of a potential reproductive health problem for women is having irregular or missed periods. Regular periods are generally a good indicator of fertility, although not always. For example, women can continue to have regular periods even when their fertility begins to decline in their 30s.
It is not known whether poor health and infertility occur in tandem from some common cause or whether one causes the other. "We don't know yet, but researchers are working on it," Dr. Moss said.
As research on fertility and infertility proceeds, Drs. Moss and Taymans said that studies exploring links between the whole genome and infertility have become increasingly important. The research now looks at how whole sets of genes behave and interact, as opposed to taking a gene-by-gene approach.
One important emerging area of research on female infertility has to do with the ovarian follicles, the small structures within the ovaries in which eggs grow and mature. Although most women were born with hundreds of thousands of these follicles, only a tiny fraction of the follicles will mature and release an egg cell. With further research, it is possible that this "ovarian reserve" could help to predict how many years a woman's fertility will continue—information she could use to help plan for a family. In addition, research is underway to explore activating dormant ovarian follicles as a possible avenue to giving infertile women additional options someday. (Read NIH-funded Researchers Generate Mature Egg Cells from Early Ovarian Follicles)
"For men, examining genetic profiles may help researchers shed light on the many unexplained cases of infertility," said Dr. Moss. New research tools give scientists ways to examine greater volumes of genetic data in detail and more quickly.
Many factors contribute to a person's fertility, and shifts accompany each stage of life. For these reasons, both Drs. Taymans and Moss said, it's not too soon to talk with a health care provider about family plans shortly after turning 20.
Among the important steps men and women can take to preserve their health and their general fertility are not smoking and maintaining a healthy weight. Staying in touch with the doctor's office is another step to add to the list.
For more information, please select the following links:
- National Infertility Awareness Week
- NICHD Division of Extramural Research
- A to Z Topics
- News Releases